1. Field of the Invention
The present invention relates to a system for providing service to an end-user terminal by means of servers like data centers. The data centers may be arranged in plural layers via a network.
2. Background
In recent years, the load on networks has increased due to large-volume contents becoming widespread, and problems including deterioration in response and decrease in communication speed have become serious. As a scheme to solve those problems, a CDN (Content Delivery Network) technique has attracted attention that is configured to distribute servers geographically or on a backbone basis instead of placing them at one site and to mirror identical contents by many servers.
For example, as shown in WO 02/054698, a CDN developed by Akamai Technologies, Inc., USA, comprises: a CDN entry point that operates instead of a content provider to be an origin; each edge node that functions as a streaming server for many end users; and a reflector node that is located in an intermediate layer between an entry point and an edge node, in order to deliver live streams as contents to end users, and when an end user is directed to an edge node that is not yet receiving a desired stream, the edge node issues a subscription request to a set of reflector nodes. If the reflector node(s) are already receiving the desired stream, the reflector node(s) send it to the requesting edge node, and if the reflector node(s) are not already receiving the desired stream, the edge node issues the subscription request up the hierarchy, ultimately reaching the entry point(s). This configuration allows the CDN to efficiently deliver the contents.
Contents that can be delivered by the above-described technique are, however, limited to data such as a video stream. In the CDN, even if a software program was delivered, a program to be downloaded to a terminal of an end user and to run in the terminal would be transmitted from a CDN entry point to an edge node via a reflector node, and transferred from the edge node to an end-user terminal, as a mere data (in the form of a file). The known CDN technique can efficiently deliver contents while avoiding load concentration on a site of a content provider, but its subject is substantially limited to data delivery.